package main

import (
    "log"
    "os"

    "gioui.org/app"
    "gioui.org/io/system"
    "gioui.org/layout"
    "gioui.org/op"
    "gioui.org/unit"
    "gioui.org/widget"
    "gioui.org/widget/material"

    "gioui.org/font/gofont"
)

func main() {
    go func() {
        w := app.NewWindow(
            app.Size(unit.Dp(600), unit.Dp(400)),
        )
        if err := loop(w); err != nil {
            log.Fatal(err)
        }
        os.Exit(0)
    }()
    app.Main()
}

func loop(w *app.Window) error {
    th := material.NewTheme(gofont.Collection())
    labels := []string{"B1", "Button2"}
    buttons := make([]widget.Clickable, len(labels))
    widgets := make([]layout.Widget, len(labels))
    var ops op.Ops
    for {
        e := <-w.Events()
        switch e := e.(type) {
        case system.DestroyEvent:
            return e.Err
        case system.FrameEvent:
            gtx := layout.NewContext(&ops, e)
            layout.Flex{Axis: layout.Vertical, Spacing: layout.SpaceAround}.Layout(gtx,
                layout.Rigid(func(gtx layout.Context) layout.Dimensions {
                    return layout.Center.Layout(gtx, func(gtx layout.Context) layout.Dimensions {
                        list := &layout.List{
                            Axis:      layout.Vertical,
                            Alignment: layout.Middle,
                        }
                        for i, label := range labels {
                            widgets[i] = material.Button(th, &buttons[i], label).Layout
                        }
                        return list.Layout(gtx, len(widgets), func(gtx layout.Context, i int) layout.Dimensions {
                            return layout.UniformInset(unit.Dp(0)).Layout(gtx, widgets[i])
                        })
                    })
                }),
                layout.Rigid(func(gtx layout.Context) layout.Dimensions {
                    return layout.Center.Layout(gtx, func(gtx layout.Context) layout.Dimensions {
                        return material.H6(th, "Info").Layout(gtx)
                    })
                }),
            )
            e.Frame(gtx.Ops)
        }
    }
    return nil
}